Dendritic arborization and spines of the neurons of the cat and human periaqueductal gray: A light, confocal laser scanning, and electron microscope study

Abstract

Neurons of the periaqueductal gray (PAG) have an extensive dendritic tree which plays an important role in the neuronal circuits supporting the functional activities of this region. The complexity of the local circuits is increased by the occurrence of dendritic spines. We have compared the dendritic and spine organization in the cat with that of man in order to verify whether an inverse relationship exists between dendritic tree extension and spine density and complexity. Sections of cat and human PAG prepared according to the Golgi-Cox method were studied with the conventional light microscope (LM) and the confocal laser scanning microscope (CLSM). The cat PAG was also studied at the electron microscopic level. The light microscopic study provided the morphoquantitative characteristics of the dendritic arborization and spines of the multipolar and fusiform neurons of the human and cat PAG. The CLSM methodology, thanks to the three-dimensional reconstruction of the neurons and the rotation of the reconstructed images, brought into view dendritic branches and spines that could not have been observed at the LM, thereby showing a wider dendritic tree and more numerous spines. The data combined from LM and CLSM demonstrate that in both species most spiny neurons are multipolar and probably projection neurons. In man, the multipolar neurons show a more extensive dendritic tree due to a wider secondary ramification, which would seem to be balanced by more numerous spines in cat. At the electron microscopic level, axo-dendritic synapses are numerous and show symmetrical and asymmetrical junctions in equal proportions; furthermore, the great majority of the spines are in contact with synaptic boutons which contain round vesicles and make predominantly asymmetrical contacts features which indicate excitatory activity. The combined use of different techniques gave a complete picture of the dendritic tree and spines of the neurons of human and cat PAG and showed a wider dendritic surface available for the receipt of the synaptic contacts than had been reported previously. Furthermore, our findings demonstrate that the PAG dendritic spines are important and specific structures in the synaptic complex of the neuropil, suggesting that they might create a local device to modulate and integrate the afferent inputs, probably in an excitatory way. The differences observed in the two species suggest that afferent information might be handled in different ways in human and cat PAG.

Altered Dendritic Spine Plasticity in Cocaine-Withdrawn Rats

“…The spine density measured using this method, 2.6 spines/μm (figure 2A), was higher than is generally reported using Golgi staining or by filling MSNs with green fluorescent protein (GFP) that in the NAcore ranges from 0.8 to 1.2 spines/μm (Robinson et al, 2001; Kolb et al, 2003; Robinson and Kolb, 2004; Ferrario et al, 2005; Chen et al, 2008; Pulipparacharuvil et al, 2008; but see Norrholm et al, 2003), as well as table S1 for comparisons between studies). In part the higher density of spines measured in the present study is due to the fact that in previous studies spines in NAcore MSNs were quantified in 2 dimensions (Feldman and Peters, 1979; Gioia et al, 1998; Gan et al, 2000). However, figure 1E reveals that even if the Z stack was collapsed and DiI-labeled dendrites quantified in 2 dimensions, spine density was higher in DiI-labeled compared with Golgi-stained dendrites (1-way ANOVA F (2,52) = 85.62, p< 0.001).…”

Determination of Axonal and Dendritic Orientation Distributions Within the Developing Cerebral Cortex by Diffusion Tensor Imaging

“…In order to construct 3-D images of cortical fields, 3-D images of the Golgi-stained tissue were acquired in reflected light mode using a 20× PLAPO NA 0.7 objective (633-nm light and a Leica SP5 AOBS microscope, Leica Microsystems, Bannockburn, IL) [62], [63]. Due to an approximately linear reduction in reflected light intensity with depth from the surface on the side proximal to the light source, it is only possible to collect data from an approximately 100- μ m-thick slab.…”

“…However, these images are not readily usable to construct 3-D models of neurons, due to significant interference from out-of-plane structures. Confocal images of back-scattered visible light [62], [63] shown in Fig. 2(d) and (e) demonstrate how the confocal technique can provide substantially improved through-plane image resolution, suitable for 3-D reconstruction procedures.…”

Multiscale imaging characterization of dopamine transporter knockout mice reveals regional alterations in spine density of medium spiny neurons

“…Furthermore, a comparison of previous LM and EM studies (Gioia et al, 1998; Harris and Stevens, 1988) on spine density demonstrates that spine density quantifications at the LM level typically underestimate spine measurements at the EM level. Because the photoconverted MSNs traced and analyzed in this study are susceptible to the same resolution limits at the LM level as classical Golgi staining, these neurons were further processed for analysis at the EM level, to ensure that many spines were not going undetected.…”